The invention relates to fastening systems for securing rails to concrete railroad ties. In particular, the invention relates to fastening systems having improved insulator spacers. The invention also relates to the improved insulator spacers. The invention further relates to methods of securing a rail to a concrete railroad tie using such an improved insulator spacer and to methods of retrofitting a railroad system having a rail insulated from a shoulder insert mounted in a concrete railroad tie using such an improved insulator spacer.
Concrete railroad ties have been used in modern railroads for many years. One of the various fastening systems that have been developed for securing rails to concrete railroad ties is shown in FIG. 1. At each rail seat area 2 where a rail 4 is to be fastened to concrete railroad tie 6, cast iron shoulder inserts 8, 10 are provided opposing each other on the field and gauge sides of the rail seat area 2, respectively. Each of the shoulder inserts 8, 10 is permanently mounted within the concrete railroad tie 6 at a position directly adjacent to the rail seat area 2. The rail 4 is mounted between the two shoulder inserts 8, 10 and upon an elastomeric tie pad 12 that spans the rail seat area 2 between the two shoulder inserts 8, 10. An insulator spacer 14 is placed adjacent to and abutting the base or toe 16 of rail 4 between rail 4 and each shoulder insert 8, 10. Each insulator spacer 14 has an inner surface that is adapted to conform to the shape of the vertical and sloping lateral faces of rail base 16. A retaining clip 18, that is attached to a shoulder insert 8, 10 by way of being inserted through a longitudinal receiving hole 20 in a shoulder insert 8, 10, presses upon the outer surface 22 of the corresponding insulator spacer 14 to rigidly secure rail 4 to concrete railroad tie 6.
In this system, the tie pad 12 and the insulator spacers 14 act to electrically insulate the rail 4 from its companion rail 4 and from the ground. Such electrical insulation is necessary to permit the rails 4 to be used to conduct electrical signals for monitoring and controlling the progress of the trains that run upon them.
However, electrical insulation is not the only important property that an insulator spacer 14 must possess. The passage of a train upon the rails 4 subjects the rails 4 to complex patterns of horizontal and vertical forces and vibrations. These forces are transmitted from the rails 4 to the fastening systems which retain the rails 4 to the railroad ties. These forces are particularly high on curved portions of the track where the laterally-directed compressive force on a shoulder insert 8, 10 may exceed 28,000 pounds. Because the insulator spacers 14 are sandwiched between the rails 4 and the shoulder inserts 8, 10, these forces subject the insulator spacers 14 to high compressive loads. To combat these loads, insulator spacers 14 have been made of a monolithic, durable insulating material having high compressive strength, such as 6-6 nylon. However, in service, the repeated exposure of the insulator spacers 14 to high compressive loads causes the insulator spacers 14 to deteriorate over time by way of crushing and abrasion. This deterioration occurs mainly in the portion of the insulator spacer 14 that is compressed between the shoulder insert 8, 10 and the vertical face of the rail base 16, a portion that is referred to as the post. As the deterioration progresses, the rail 4 becomes able to move, thus causing wear and fatigue on the fastening system components and the concrete railroad tie 6 and compromising the safety of train travel upon the rail 4. Thus, the deterioration makes it necessary to spend time and money to inspect the insulator spacers 14 for wear and to remove and replace worn insulator spacers 14.
It is to be understood that what is being referred to herein by the term insulator spacer is also referred to by those skilled in the art by the simple generic term insulator. However, the term insulator spacer is more descriptive as it brings to mind both the mechanical and electrical functions of the component.
The present invention overcomes the problems associated with the insulator spacer deterioration described above by providing an improved fastening system for securing a rail to a concrete railroad tie that employs an improved insulator spacer. The improved insulator spacer has at least one composite insert located in an area of the improved insulator spacer that is subjected to high compressive loads in service. The composite insert or inserts are located and sized so that together the composite inserts carry most of the laterally-directed compressive load that is exerted in service upon the improved insulator spacer by the rail and the shoulder insert. The composite insert or inserts have a compression fatigue lifetime that is substantially longer than that of the material of the improved insulator spacer body that contains the composite insert. The composite insert or inserts are sufficiently electrically insulating so as to operably electrically isolate the rail the improved insulator spacer is in contact with from the shoulder insert the improved insulator spacer is also in contact with.
Thus, described is a fastening system for securing a rail to a concrete railroad tie wherein the concrete railroad tie has a rail seat area on which the rail rests. The fastening system comprises a shoulder insert mounted in the concrete railroad tie adjacent to the rail seat area, an improved insulator spacer inserted between the shoulder insert and the rail, and a retaining clip attached to the shoulder insert. The improved insulator spacer has a post and also has a composite insert positioned in the post so that the shoulder insert and the rail each contact the composite insert.
The composite insert is designed to place wear resistant, durably tough material in contact with the adjacent surfaces of the rail and the shoulder insert thereby enhancing the mechanical lifetime of the improved insulator spacer of which it is a part. The composite insert also has high compressive strength, electrically insulating material sandwiched between its tough outer layers to provide electrical insulation between the rail and the shoulder insert.
An improved insulator spacer having at least one such composite insert is also described.
Also described is a method of securing a rail to a concrete railroad tie. This method comprises the step of inserting an improved insulator spacer between a rail and a shoulder insert which is mounted in a concrete railroad tie. The improved insulator spacer used in this method has a post having a composite insert positioned in the post so that the shoulder insert and the rail each contact the composite insert.
Also described is a method of retrofitting a railroad system that has a rail insulated by means of an existing insulator spacer from a shoulder insert which is mounted in a concrete railroad tie. This method comprises the steps of first removing the existing insulator spacer and then inserting between the rail and the shoulder insert an improved insulator spacer which has a post having a composite insert positioned therein so that the shoulder insert and the rail each contact the composite insert.
Other features and advantages inherent in the subject matter claimed and described will become apparent to those skilled in the art from the following detailed description of presently preferred embodiments thereof and to the appended drawings.